U.S. patent number 4,692,798 [Application Number 06/689,243] was granted by the patent office on 1987-09-08 for apparatus and process for improving visibility of object within visual field.
This patent grant is currently assigned to Nissan Motor Company, Limited. Invention is credited to Yuichi Abe, Yasutoshi Seko.
United States Patent |
4,692,798 |
Seko , et al. |
September 8, 1987 |
Apparatus and process for improving visibility of object within
visual field
Abstract
An apparatus for improving the visibility of objects within the
visual field of a vehicle driver and a process therefor are
disclosed. The apparatus includes a light caster casting intense
visible light toward a reflective object at a frequency no lower
than critical fusion frequency, an image pickup device picking up
an image of the object and outputting corresponding image data, an
image data amplifier, a picture signal generator and a display. The
image data are processed to yield a picture signal which yields a
clear picture of the object on the display. The apparatus can give
the driver of a vehicle a clear picture of the objects within
forward visual field of the vehicle at night without dazzling the
drivers of vehicles in the opposite lane.
Inventors: |
Seko; Yasutoshi (Yokohama,
JP), Abe; Yuichi (Yokosuka, JP) |
Assignee: |
Nissan Motor Company, Limited
(Yokohama, JP)
|
Family
ID: |
26334992 |
Appl.
No.: |
06/689,243 |
Filed: |
January 7, 1985 |
Foreign Application Priority Data
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Jan 9, 1984 [JP] |
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59-1717 |
Jan 9, 1984 [JP] |
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59-1719 |
|
Current U.S.
Class: |
348/118;
250/461.1; 348/148; 349/1; 349/72 |
Current CPC
Class: |
B60Q
1/14 (20130101); B60R 1/00 (20130101); H04N
5/238 (20130101); H04N 5/2354 (20130101); B60R
2300/8053 (20130101); B60R 2300/106 (20130101) |
Current International
Class: |
B60Q
1/08 (20060101); B60Q 1/04 (20060101); B60R
1/00 (20060101); H04N 007/18 (); H04N
005/225 () |
Field of
Search: |
;340/50,81R,84,902,904
;358/93,108,213,228 ;362/61,64,321 ;356/23-26 ;252/582
;350/330,331R |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
|
1176179 |
|
Aug 1964 |
|
DE |
|
49-72830 |
|
Jul 1974 |
|
JP |
|
52-101526 |
|
Aug 1977 |
|
JP |
|
Primary Examiner: Britton; Howard W.
Assistant Examiner: Peng; John K.
Attorney, Agent or Firm: Schwartz, Jeffery, Schwaab, Mack,
Blumenthal & Evans
Claims
What is claimed is:
1. An apparatus comprising:
means for casting visible light toward a reflective object at a
frequency of no less than the critical fusion frequency;
means for picking up an image of the object and outputting image
data in accordance with the picked-up image;
a light-intensity sensor monitoring the intensity of a light
incident on said image pickup means and outputting a signal
representing the level of the intensity of the incident light;
an optical shutter of liquid crystal filtering the incident
light;
a light-intensity control circuit opening and shutting said optical
shutter in accordance with the frequency of the casting of the
visible light and controlling a duty cycle of said optical shutter
in response to a level of said signal so as to control an effective
transmissivity of said optical shutter;
means for generating a picture signal in accordance with the image
data; and
means for displaying a picture of the object in response to the
picture signal.
2. An apparatus as recited in claim 1, wherein said light casting
means includes means for generating a flashing visible light.
3. An apparatus as recited in claim 1, wherein said display means
is a raster scan-type cathode ray tube.
4. An apparatus as recited in claim 1, wherein the light-intensity
control circuit includes a circuit categorizing the level of light
intensity among a plurality of levels and a plurality of one-shot
multivibrators which output pulses with unique widths monotonically
related to the categorized light intensity, the output pulse
serving to control the open period of the optical shutter.
5. An apparatus as recited in claim 1, wherein the light-intensity
control circuit includes a circuit for dividing an output range of
the level of light intensity among a plurality of levels and a
circuit adjusting the transmissivity of the liquid crystal shutter
in response to the output of the level-dividing circuit.
6. An apparatus as recited in claim 1, wherein the liquid crystal
shutter is of the field-effect type.
7. An apparatus as recited in claim 1, further comprising an
optical shutter for said image pickup means driven to open
synchronously with the intervals of transmission of visible light
and wherein said visible light casting means casts visible light
stroboscopically at said frequency.
8. An apparatus as recited in claim 1, wherein said image pickup
means comprises a solid state image sensor which includes a
photoelectronic device.
9. An apparatus as recited in claim 8, wherein the photoelectronic
device has an amplified output.
10. An apparatus as recited in claim 9, wherein the solid state
image sensor is a CCD image sensor.
11. An apparatus as recited in claim 9, wherein the photoelectronic
device is a phototransistor.
12. A process comprising the steps of:
casting visible light toward a reflective object at a frequency no
less than the critical fusion frequency;
picking up an image of the object;
outputting image data in accordance with the image;
monitoring the intensity of an incident light in said image pickup
step and outputting a signal representing the level of the
intensity of the incident light;
filtering the incident light by means of an optical shutter;
opening and shutting the optical shutter in accordance with the
frequency of the casting of visible light and controlling the duty
cycle of said optical shutter in response to a level of said signal
so as to control an effective transmissivity of said optical
shutter;
generating a picture signal in accordance with the image data;
and
displaying a picture of the object in response to the picture
signal.
13. An apparatus for improving the visibility of an object within a
visual field of a vehicle comprising:
a light caster casting visible light toward a reflective object
within the visual field stroboscopically at a frequency no less
than critical fusion frequency;
means for picking up an image of the object and outputting image
data;
a light intensity sensor sensing the intensity of a light incident
on said image pickup means and for outputting a signal representing
the level of the intensity of the incident light;
an optical shutter for said image pickup means driven to open
synchronously with the intervals of transmission of the strobed
visible light;
a light-intensity control circuit driving said optical shutter and
controlling the duty cycle of said optical shutter in response to a
level of said signal so as to control an effective transmissivity
of said optical shutter;
a picture signal generator outputting a picture signal in
accordance with the image data; and
a display presenting a picture of the object in response to the
picture signal.
14. An apparatus as recited in claim 13, wherein the optical
shutter is divided into a plurality of elements arranged laterally
across the vehicle.
15. An apparatus comprising:
means for casting visible light toward a reflective object at a
frequency no less than the critical fusion frequency;
means for picking up an image of the object and outputting image
data in accordance with the picked-up image;
a light intensity sensor monitoring the intensity of a light
incident on said image pickup means and outputting a signal
representing the level of the intensity of the incident light;
an optical shutter of a field-effect type liquid crystal filtering
the incident light;
a light-intensity control circuit analogically controlling a drive
voltage of the field-effect type liquid crystal in response to a
level of said signal so as to control an instantaneous
transmissivity of said optical shutter;
means for generating a picture signal in accordance with the image
data; and
means for displaying a picture of the object in response to the
picture signal.
16. An apparatus as recited in claim 15, wherein said
light-intensity control circuit includes a circuit for dividing an
output range of the level of light intensity among a plurality of
levels and a circuit analogically controlling the drive voltage of
the field-effect type liquid crystal in response to an output of
the level-dividing circuit.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and process for
improving the visibility of objects within a visual field and in
particular to an apparatus and process for use in an automotive
vehicle under adverse optical conditions.
2. Description of the Prior Art
Currently, the most common method of improving the visibility of
objects within a forward visual field of an automotive vehicle
during night driving is to increase the intensity of light cast by
the headlights. However, the intensified headlights tend to dazzle
the drivers of vehicles in the opposite lane.
Japanese published unexamined patent application No. 49-72830
discloses a system for reducing the transmission of intensified
headlight cast by an automotive vehicle in the opposite lane
through a vehicular windshield by means of an optical filter with
adjustable transmissivity e.g., a liquid crystal panel and an
electronic circuit for controlling the transmissivity of the
optical filter. However, since this system darkens the forward
visual field of the vehicle on which the headlight is incident, at
the moment the optical filter transmissivity is reduced, the driver
of the filtering vehicle may fail to recognize pedestrians, etc.
crossing or standing in the road within the forward visual
field.
Japanese published unexamined patent application No. 52-101526 also
discloses a system for shutting out the headlight cast by a vehicle
in the opposite lane. However, this system is less effective in
cases where the vehicle in the opposite lane lacks the same
polarizing filters or plates as are used on one's own vehicle.
Generally, it is known that, when an object is illuminated
stroboscopically at a low frequency, an observer will see a
flickering image of the illuminant, but if the on-off frequency of
the illuminant is increased to a certain value, the observer will
have a steady image of the illuminant. With reference to human
eyesight, this effect is quanitized in Talbot-Plateau's law:
##EQU1## wherein L.sub.m is steady luminance with time and L(t) is
varying luminance with time. In addition, the critical fusion
frequency (hereinafter refer to as CFF) at which an observer will
perceive a steady image of the illuminant can be derived from
Ferry-Porter's law as follows:
wherein a and b are constants.
SUMMARY OF THE INVENTION
One consequence of Talbot-Plateau's law is that it is possible to
cast visible light at a high intensity toward the driver of a
vehicle in the opposite lane at a frequency higher than the CFF
without dazzling the driver.
An object of this invention is to provide an apparatus for
improving the visibility of objects within a visual field.
Another object of this invention is to provide an apparatus for
improving the visibility of objects within a forward visual field
of a vehicle at night. In order to achieve these objects, the
apparatus of this invention includes a light caster casting
intensified visible light toward a reflective object at a frequency
higher than critical fusion frequency, an image pickup device,
e.g., a solid state image sensor or photomultiplier, for picking up
an image of the object and outputting corresponding image data, and
an image data amplifier. The image data are processed to yield a
picture signal which yields a clearer picture of the object on a
display.
A further object of this invention is to provide an apparatus for
improving the visibility of objects within a visual field which can
filter out optical noise and particularly prevent blooming in a
solid state image sensor serving as an image pickup means. In order
to achieve this object, the apparatus of this invention includes a
light caster casting intensified visible light stroboscopically at
a frequency equal to or higher than the critical fusion frequency
toward a reflective object, an image pickup device, e.g., a solid
state image sensor for picking up an image of the object and
outputting corresponding image data, an image data amplifier and an
optical shutter for the image pickup device driven to open
synchronously with the active period of the stroboscopic visible
light. The image data are processed to yield a picture signal which
gives a clearer picture of the object on a display without
generating any saturated areas wholly lacking in contrast.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph illustrative of Talbot-Plateau's law underlying
the present invention.
FIG. 2 is a block diagram of a first embodiment of a system for
improving the visibility of objects within a visual field according
to the present invention.
FIG. 3 is a block diagram of a CCD image sensor used as an image
device in FIG. 2.
FIG. 4 is a timing chart illustrative of the operation of the CCD
image sensor of FIG. 3.
FIG. 5 is a cross-section through a light caster of FIG. 2.
FIG. 6 is a flowchart illustrative of a image data cumulating
process according to the system of FIG. 2.
FIG. 7 is a timing chart illustrative of the image data cumulating
process according to the system of FIG. 2.
FIG. 8 is a timing chart illustrative of a image data cumulating
process according to a second embodiment of a system for improving
the visibility of objects within a visual field according to the
present invention.
FIG. 9 is a plan view of a first modification to the light caster
of FIG. 5.
FIG. 10 is a section taken along the line X--X in FIG. 9.
FIG. 11 is a perspective view of a second modification to the light
caster of FIG. 5.
FIG. 12 is a diagram of a third modification to the light caster of
FIG. 5.
FIG. 13 is a schematic section of a fourth modification to the
light caster of FIG. 5.
FIG. 14 is a block diagram of a third embodiment of a system for
improving the visibility of objects within a visual field according
to the present invention.
FIG. 15 is a perspective view of the liquid crystal shutter of FIG.
14.
FIG. 16 is an illustration of a light intensity detector of FIG.
14.
FIG. 17 is a timing chart illustrative of the operation of the
system of FIG. 14.
FIG. 18 is a diagram of a modification to the transmitted light
intensity control circuit of FIG. 14.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIGS. 2 to 18, the preferred embodiments of this
invention will be described hereinafter in detail.
As shown in FIG. 2, the first embodiment of an apparatus according
to this invention comprises an image pickup device 1, an A/D
converter 2, an image data cumulation processor 3, a video signal
generator 4, a display 5, a light caster 6, a drive circuit 7 for
the light caster 6, and a clock 8.
The image pickup device 1 is a solid state image sensor, e.g., a
CCD image sensor such as is shown in FIG. 3, or a photomultiplier.
The image pickup device 1 serves to pick up images of objects
situated beyond the naked-eyes visual range of the driver of a
vehicle. The CCD image sensor, as illustrated in FIG. 3, includes a
number of picture elements (pixels) arranged 2-dimensionally on a
light-receiving surface of the CCD image sensor. For example, there
may be 78,080 pixels, i.e., 320 columns by 244 rows. Each picture
element consists of a photoelectronic device 11a or 11b and a
vertical shift register 12a or 12b. The photoelectronic device 11a
or 11b preferably is a device effecting current amplification,
e.g., a phototransistor. Alternatively, a device not effecting
current amplification, e.g., a photodiode may be used in a system
performing an image data cumulation.
A series of horizontal shift registers 13a and 13b are connected to
the output ends of the 320 columns of vertical shift registers 12a
and 12b. Both groups of photoelectronic devices 11a and 11b receive
a write clock pulse train C1 which, when its level is low, allows
the charges generated in the photoelectronic devices 11a or 11b to
be transferred into the enabled vertical shift register 12a or 12b.
The two groups of vertical shift registers 12a and 12b receive
first and second vertical register and shift pulse trains S1 and S2
respectively consisting of register pulses and shift pulses. As
shown in FIG. 4, the second vertical register and shift pulse train
S2 is the logical inverse of the first vertical register and shift
pulse train S1. Likewise, the two groups of horizontal shift
registers 13a and 13b receive first and second horizontal register
and shift pulse trains S3 and S4 respectively, which are also
logical inverts. All of the different pulse trains C1, S1, S2, S3
and S4 are formed from clock pulses generated by the clock 8. At
least 244 shift pulses of each of the first and second vertical
register and shift pulse trains S1 and S2 occur between successive
pulses of the write clock pulse train C1, corresponding to the
number of the picture element rows. Likewise, at least 320 shift
pulses of each of the first and second horizontal register and
shift pulse trains S3 and S4 occur between successive shift pulses
of the first and second vertical register and shift pulse trains S1
and S2.
The operation of the CCD image sensor of FIG. 3 will be described
hereinafter in conjuction with the timing chart of FIG. 4. As shown
in FIG. 4, coincident with the first (low-going) pulse 14 of the
write clock pulse train C1, the voltage level of the second
vertical register and shift pulse train S2 is high, thus enabling
the second group of vertical shift registers 12b, the electrical
charge generated in each photoelectronic device 11b is transferred
into a corresponding vertical shift register 12b. At the same time,
since the voltage level of the first vertical register and shift
pulse train S1 is low, thus disabling the first group of vertical
shift registers 12a, transfer of the electrical charge generated in
each photoelectronic device 11a to the corresponding vertical shift
register 12a is inhibited.
A negative shift pulse 17 of the second vertical register and shift
pulse train S2 following the clock pulse 14 induces the transfer of
the electrical charge stored in each vertical shift register 12b to
the next vertical shift register 12a, i.e. upwards one step as
viewed in FIG. 3. At the same time, a positive shift pulse 18 of
the first vertical register and shift pulse train S1 shifts the
electrical charge stored in each vertical shift register 12a to the
next vertical shift register 12b. Thus, in response to a given
number, e.g. 244, of shift pulses 17, 18, all of the picture
element outputs transferred into the vertical shift registers 12a
and 12b from the devices 11b are eventually transferred to the
horizontal shift registers 13a and 13b. The horizontal shift
registers 13a and 13b are all driven by the first and second
horizontal register and shift pulse trains S3 and S4, so that the
horizontal shift register 13b at the output terminal of the series
of horizontal shift registers 13a and 13b eventually sends the
image data cumulation processor 3 a train of 39,040 picture element
outputs, i.e., the image data for one frame, with each pulse of the
write clock pulse train C1 via the A/D converter 2.
Following transfer and output of the "b"-group pixel charges in
response to clock pulse 14, a second clock pulse 20 falls
coincident with a register pulse 19, which enables the electrical
charges generated in the photoelectronic devices 11a to be
transferred to corresponding each vertical shift registers 12a.
Subsequent processes are performed in the same manner as for the
"b"-group of photoelectronic devices and vertical shift registers.
The register pulses 19 are generated synchronously with every
second clock pulse 20, so that the "a" and "b" pixel rows are
sampled and output alternatingly in accordance with the
requirements for the interlaced raster scan of a conventional CRT
display.
Thus, the CCD image sensor outputs the pulse-amplitude modulated
image data for all 78,080 picture elements in a pre-arranged
sequence by the time it receives the third pulse of the write clock
pulse train C1. In practice, a waveforming circuit and a noise
eliminating circuit are connected to the output terminal of the
series of horizontal shift registers 13a and 13b. However, since
these circuits are not essential to this invention, description of
these circuits will be omitted.
The A/D converter 2 connected to the output terminal of the image
pickup device 1 converts the train of analog picture element
outputs to a corresponding digital pulse train.
The light caster 6 is designed to a cast flashes of visible light
at a frequency higher than CFF (Critical Fusion Frequency). As
illustrated in FIG. 5, the light caster 6 has a housing 21, a lamp
22 fixed to the housing 21 and serving as a continuous light
source, a parabolic reflector 23 fixed relative to the lamp 22, a
strobe disc 24 having slits 25 and disposed in front of the
reflector 23, a stepping motor 26 for the strobe disc 24 driven by
the drive circuit 7 at a rate determined by a clock pulse train C2
from the clock 8, a transparent cover 27 over the front of the
housing 21, and a convex lens 28 fixed in the cover 27.
The light caster 6 is used as a headlight of the vehicle. The
luminosity of the lamp 22, the number of slits 25 and/or the speed
of rotation of the stepping motor 26 are suitably selected so as to
match the range and illumination of a conventional headlight.
Stroboscopic visible light reflected by any objects in the forward
visual field of the vehicle falls on the image pickup device 1.
The clock 8 provides the drive circuit 7, the image pickup device
1, the image data cumulation processor 3, the video signal
generator 4, and the display 5 with clock pulse trains C2, C3 and
C4. The clock pulse train C2 serves to drive the stepping motor 26
as previously stated. The clock pulse train C3 is converted to a
suitable frequency by frequency dividers, not shown, in the image
pickup device 1, the image data cumulation processor 3, the video
signal generator 4 and the display 5. For example, the clock pulse
train C3 provides the base frequency for the write clock pulse
train C1, the vertical register and shift pulse trains S1 and S2
and the horizontal register and shift pulse trains S3 and S4 in the
image pickup device 1. Additionally the clock pulse train C3 serves
as a synchronization signal for the image data cumulation processor
3, a video signal generated by the video signal generator 4, and
the display 5. The clock pulse train C4 serves as a read-out pulse
for a memory 29, a signal controlling a scan signal for the video
signals from the video signal generator 4 (i.e., determinations of
timing of vertical retrace interval and horizontal retrace
interval), or a synchronization signal for the video signal between
the image data cumulation processor 3 and the display 5.
The image data cumulation processor 3 will in practice be a
microcomputer including an input interface 30, an output interface
31, a CPU 32 and the memory 29. The input interface 30 is connected
to the A/D converter 2. The output interface 31 is connected to the
video signal generator 4.
The operation of the image data cumulation processor 3 will be
described in detail in conjunction with FIGS. 6 and 7. Suppose the
image pickup device 1 and the display 5 have three picture elements
for simplified illustration. As the light caster 6 casts the
strobed visible light forward of the vehicle synchronously with the
clock pulse train C2, the image pickup device 1 picks up an image
of the entire forward visual field in the strobed visible light
reflected by objects in the field. A pulse train made up of the
digitalized picture element outputs of this image of the forward
visual field, as shown in FIG. 7, is sent to the input interface 30
through the A/D converter 2.
According to this embodiment, the video signals for each frame are
obtained substantially synchronously with an transmission interval
of the strobed visible light (in practice, with some delay) and one
memory reset pulse C4 is generated after every i video frames,
where the number i is chosen to be small enough that the visual
field image will remain essentially constant.
As shown in FIG. 6, the image data cumulation program starts with
an initialization operation at a step 101. This operation clears
and allocates a memory area for the train of picture element
outputs outputted from the image pickup device 1 through the A/D
converter 2. Upon completion of the step 101, the program advances
to a step 102. The step 102 checks for the occurrence of a clock
pulse C4. In response to a clock pulse C4, the program advances to
a step 105. On the other hand, in the absence of clock pulse C4,
the program advances to a step 103. The operation at the step 103
checks for receipt of a picture element output at the input
interface 30, in which case the program advances to a step 104. The
program repeats the step 103 until the next picture element output
is sent to the input interface 30.
The operation at the step 104 is as follows: each newly-received
picture element output B1(n), B2(n), and B3(n), where n represents
the interval between the (n-1)th and nth occurrences of the reset
pulse C4, are added to the integrated picture element values
A1(n-1), A2(n-1) and A3(n-1) which have been cumulated in memory
prior to the (n-1)th occurrence of the reset pulse C4. The
resulting values, i.e., the n-times-cumulated picture element
values {Aj(n)=Aj(n-1)+Bj(n-1)} are substituted for the
(n-1)-times-cumulated values Aj(n-1) stored in the memory 29,
wherein n=1, 2, 3, . . . through i, representing the current sample
period after the last occurrence of the reset pulse C4 and j=1, 2
and 3, representing the pixels.
Upon completion of step 104, controls returns to step 102. Thus, as
the program loops through the steps 102, 103 and 104, the picture
element outputs at each pixel are cumulated over a given number of
sample frames, e.g. i (See the 4th chart from top in FIG. 7). Upon
receipt of a reset pulse C4, the program switches to the step 105
as previously stated. The step 105 outputs the cumulated picture
element values to the video signal generator. The step 106
following the step 105 clears the cumulated picture element values
stored in a picture element area of the memory 29. The image data
cumulation processor 3 may alternatively send the video signal
generator the digitalized cumulated image data after each fixed
unit of distance travelled by the vehicle.
The video signal generator 4 converts the digitalized cumulated
image data into video signals which drive the display 5.
The display 5 may be, for example, a CRT, especially a raster scan
type CRT, or a liquid crystal display. The display 5 can display
the images of the objects beyond the naked-eye visual range of the
driver of the automotive vehicle. The display 5 may be suitably
located near the driver seat.
A second embodiment of this invention will be described hereinafter
with reference to FIGS. 8 to 10. Elements similar to those used in
the first embodiment of this invention will not be discussed again.
In the second embodiment, a light caster 6A casts a continuous
visible light beam forward of an automotive vehicle while
intermittently shifting the light beam from side to side at a
switching frequency exceeding the CFF.
The light caster 6A comprises a hexagonal case 32, a lamp 33
emitting light continuously, a rotary parabolic reflector 34, a
stepping motor 35 for the reflector 34 and six optical fiber
bundles 36a, 36b, 36c, 36d, 36e and 36f. The hexagonal case 32 has
six faces, each optically connected to the end of one of the
optical fiber bundles 36a to 36f and serves to distribute the
continuous visible light beam among the optical fiber bundles
36a-f. The lamp 33 is fixed to the hexagonal case 32 at the focus
of the reflector 34. The reflector 34 rotates through 60.degree.
clockwise as viewed in FIG. 9 at regular intervals so that it is
always directly facing the end of one of the optical fiber bundles
36a, 36b, 36c, 36d, 36e or 36f at a time. The stepping motor 35 is
driven by the drive circuit 7. The output ends of the six optical
fiber bundles 36a to 36f are directed forward of the vehicle and
serve as cooperatively as a headlight. A group of three of the
output ends of the optical fiber bundles 36a to 36c are directed
slightly upwards in FIG. 9 and the other group of three optical
fiber bundles 36d to 36f are directed slightly downwards in FIG. 9,
that is, right and left respectively.
Changes in the operation of the image data cumulation processor 3
will be described in connection with the second embodiment of this
invention in conjunction with the timing chart of FIG. 8. As the
direction of the cast visible light beam changes at a frequency
exceeding the CFF, the electric charge induced in each
photoelectronic element 11a changes accordingly. Thus, the train of
picture element outputs from the image pickup device 1 is somewhat
different from that in the first embodiment of this invention, as
shown on the third chart from top in FIG. 9. Assume that the image
pickup device 1 and the display 5 have six picture elements.
The third chart from top in FIG. 8 shows exemplary image data
trains output by the image pickup device 1, each consisting of
three picture element output. The first image data train consists
of a first high-level picture element output 37, a third
intermediate-level picture element output 38 and a low-level fifth
picture element output 39. The second image data train consists of
a second high-level picture element output 40 at a level higher
than the intermediate level but lower than the high level in the
first image data train, a fourth picture element output 41 at a
level equal to that of the second picture element output 40, and a
sixth picture element output 42 at a level higher than the low
level but lower than the immediate level in the first image data
train.
The third image data train is an updated version of the first image
data train. The first picture element output 37 drops to the
intermediate level of the first image data train, the third picture
element output 38 rises to the high level of the first image data
train, and the fifth picture element output 39 rises to the
intermediate level of the first image data train.
The fourth image data train similarly corresponds to the second
image data train. The second picture element output 40 drops to the
low level of the second image data, the fourth picture element
output 41 remains high, and the sixth picture element output 42
rises to the high level of the second image data.
Changes in the levels of the first, third and fifth picture element
outputs 37, 38 and 39 will tend to match those of the second,
fourth and sixth picture element outputs 40, 41 and 42 in
successive image data trains. As shown on the fifth chart from top
in FIG. 8, the two group of picture element outputs are cumulated
over about four frames, and then are cleared in response to a reset
pulse C4.
The reset pulse period is equal to the period in which the light
beam switches between optical fiber bundles 36a-f. In response to
the reset pulse C4, the image data cumulation processor 3 sends the
digitalized cumulated image data to the video signal generator 4
(See the chart at bottom in FIG. 8) and clears the contents of the
memory 29.
In the second embodiment of this invention, the scanning light beam
enhances the absolute luminosity in the forward visual field of the
vehicle so as to yield a clearer picture on the screen of the
display 5 than in the first embodiment.
FIG. 11 illustrates a second modification to the light caster 6.
The light caster comprises a fixed lamp 51 emitting light
continuously, a rotary cylindrical reflector 52 having a
transparent window 53, a stepping motor 54, and speed-up gears 55.
The stepping motor 54 rotates the reflector 52 by means of the
speed-up gears 55.
FIG. 12 illustrates a third modification to the light caster 6. The
light caster comprises a fixed lamp 56 emitting light continuously,
a parabolic reflector 57 and an electromagnetic shutter 58 in front
of the lamp 56. The shutter 58 is driven by the drive circuit 7 and
opens and shuts at a frequency not less than CFF in response to a
timing signal from the clock 8. This modification obviates the need
for a rotary driver.
FIG. 13 illustrates a fourth modification to the light caster 6.
The light caster is a combined dimbeam headlight and cruising
headlight and comprises a fixed lamp 60 emitting light
continuously, a fixed parabolic reflector 61 focussed on the lamp
60, four mirrors 62, 63, 64 and 65, a first optical fiber 66 for
the dimmer headlight, a second optical fiber 67 for the brighter
headlight, a dim-beam headlight 68 in the form of a spherical lens,
a crusing headlight 69 in the form of a spherical lens, a headlight
reflector 70 and a front glass cover 71 for the headlight reflector
70. The mirror 62 is a fixed 90.degree.-reflecting mirror facing
the lower part of the reflector 61 in FIG. 13. The mirror 62
deflects half of the light from the reflector 61 to the other
headlight system, not shown, e.g., the left-hand headlight system.
As the mirror 65 rotates clockwise as viewed in FIG. 13, its
opposite surfaces alternatingly reflect the light from the
reflector 61 toward one of the mirrors 63 and 64. These latter
mirrors 63, 64 are fixed 90.degree.-reflecting mirrors and inject
light from the mirror 65 into the corresponding first or second
optical fiber 66 or 67. The dim-beam headlight 68 and the cruising
headlight 69 are situated at or near the focus of the headlight
reflector 70. In this modification, the rotary mirror 65 alternates
between the dim-beam and high-beam headlights at a frequency not
less than CFF.
According to this modification, the lamp 60 can be located
arbitrarily, so that replacement of the lamp 60 can be
facilitated.
Referring to FIGS. 14 to 17, a third embodiment of this invention
will be described hereinafter. Description of elements similar to
those used in the first embodiment of this invention will not be
repeated.
As shown in FIG. 14, the third embodiment of an apparatus according
to this invention comprises an image pickup device 1, an A/D
converter, not shown, connected to an output terminal of the image
pickup device 1, a video signal generator 4, a display 5, a light
caster 6, a drive circuit 7 for the light caster, a clock 8, a
liquid crystal shutter 80, a light-intensity sensor 81 and a
transmitted light-intensity controller 82. This apparatus lacks the
image data cumulation processor used in the first and second
embodiments of this invention. Stroboscopic visible light cast by
the light caster 6 is reflected by objects within the forward
visual field of a vehicle and then enters the image pickup device 1
via the liquid crystal shutter 80 and the light intensity sensor
81.
The liquid crystal shutter 80 consists of three liquid crystal
panels 80a, 80b and 80c arranged laterally across the vehicle. The
liquid crystal panels 80a, 80b and 80c are connected to output
terminals of respective transmitted light-intensity control
circuits 82a, 82b and 82c of the transmitted light-intensity
controller 82. As illustrated in FIG. 15, each of the liquid
crystal panels 80a, 80b and 80c is composed of two transparent
glass panels 83 and 84 and a hollow spacer 85 disposed between the
glass panels 83 and 84. Each glass panel 83 or 84 has a transparent
electrode, not shown, on its inner surface. A pair of the
electrodes is connected to a voltage terminal 86a, 86b or 86c. Each
pair of electrodes of the liquid crystal panels 80a, 80b and 80c is
independent of others. The spacer 85 contains a field-effect liquid
crystal within its hollow interior. A drive voltage applied to the
voltage terminal 86a, 86b or 86c changes the light transmissivity
of the corresponding liquid crystal panel 80a, 80b or 80c.
The light intensity sensor 81, as illustrated in FIG. 16, comprises
three convex lenses 87a, 87b and 87c, three camera cones 88a, 88b
and 88c each supporting the lenses 87a, 87b and 87c, and three
photoelectronic devices 89a, 89b and 89c each disposed in the focal
planes of the lenses 87a, 87b and 87c. Each of the photoelectronic
devices 89a, 89b and 89c is a current amplification device, e.g., a
phototransistor. Some of the light incident on the liquid crystal
panels 80a, 80b and 80c enters each of the lenses 87a, 87b and 87c.
The output of each of the photoelectronic devices 89a, 89b and 89c
is sent to a corresponding transmitted light-intensity control
circuit 82a, 82b or 82c.
The transmitted light-intensity controller 82 will be described in
conjunction with FIG. 14. Since the transmitted light-intensity
control circuits 82a, 82b and 82c are identical, only the first
transmitted light-intensity control circuit 82a will be described.
The transmitted light-intensity control circuit 82a comprises a
high-level comparator 90a, an intermediatelevel comparator 90b and
a zero-level comparator 90c which cooperate to divide the output
range of the photoelectronic device 89a into three stages
respectively lower-bounded by the high reference voltage V.sub.1,
an intermediate reference voltage V.sub.2 and a zero reference
voltage. The outputs of the comparators 90a, 90b and 90c are
processed by a decoder 91 which comprises two inverters 92 and 93
and two AND gates 94 and 95. The outputs of the decoder 91 are
applied to AND gates 96, 97 and 98 as gate signals. The output of a
first one-shot multivibrator 110 is applied to the AND gate 96, the
output of a second one-shot multivibrator 111 is applied to the AND
gate 97 and the output of a third one-shot multivibrator 112 is
applied to the AND gate 98. All of the outputs of the one-shot
multivibrators 110, 111 and 112 are synchronous with a clock pulse
C5 from the clock 8 and the transmission interval of the strobed
visible light. The first one-shot multivibrator 110 outputs a pulse
with a narrow width, the second one-shot multivibrator 111 outputs
a pulse with an intermediate width and the third one-shot
multivibrator 112 outputs a relatively wide pulse. The outputs of
all of the AND gates 96, 97 and 97 are applied to an OR gate 113,
the output of which is conducted to a drive circuit 114. The output
of the drive circuit 114 is provided to the voltage terminal 86a of
the first liquid crystal panel 80a.
As shown on the first, second and third charts of FIG. 17, as the
light intensity at the photoelectronic device 89a increases with
time, first the output of the intermediate-level comparator 90b
steps up and then the output of the high-level comparator 90a steps
up, and then as the light intensity at the photoelectronic device
89a decreases with time, first the output of the high level
comparator 90a steps down and then the output of the intermediate
level comparator 90b steps down. The output level of the zero level
comparator 90c remains high throughout.
The AND gate 98 outputs wide pulses until the output of the
intermediate-level comparator 90b goes high. The AND gate 97
outputs intermediate-width pulses starting in response to the
rising edge of the output of the intermediate-level comparator 90b
and ending in response to the rising edge of the output of the
high-level comparator 90a or the trailing edge of the former
signal. The AND gate 96 outputs narrow pulses as long as the output
of the high level comparator 90a remains high. Thus, as the
intensity of incident light on the liquid crystal panel 80a rises,
the duty cycle of the liquid crystal panel 80a drops so as to
reduce its effective transmissivity. The transmitted light
intensity control circuits 82b and 82c operate in the same manner
as the transmitted light intensity control circuit 82a. For
example, in cases where a vehicle in the opposite lane casts a very
intense beam toward regions within the forward visual field of
one's own vehicle corresponding to one of the crystal panels 80a,
80b or 80c, that liquid crystal panel would reduce its effective
transmissivity, thus preventing "blooming" in the solid state
pickup image sensor and the display. The digitalized picture
element outputs are applied directly to the video signal generator
4 without any image data cumulation processing.
FIG. 18 shows a modification to the transmitted light intensity
control circuits 82a, 82b and 82c. This modification is designed to
adjust the drive voltage of the liquid crystal panels 80a, 80b or
80c to any of three levels. The output of the comparator 90a is
applied to the ON-OFF control terminal of a high-level analog
switch 116, the output of the comparator 90b is applied to the
ON-OFF control terminal of an intermediate-level analog switch 117
and the output of the comparator 90c is applied to the ON-OFF
control terminal of a low-level analog switch 118. The input
terminal of the high-level analog switch 116 receives a high drive
voltage V.sub.3 via a resistor voltage divider 119. The input
terminal of the intermediate-level analog switch 117 receives an
intermediate drive voltage V.sub.4 via the resistor voltage divider
119. The input terminal of the low-level analog switch 118 receives
a low drive voltage V.sub.5 via the resistor voltage divider 119.
All of the drive voltages V.sub.3, V.sub.4 and V.sub.5 are higher
than the reference voltages V.sub.1 and V.sub.2. All of outputs of
the analog switches 116, 117 and 118 are applied to an addition
circuit 120. The output of the addition circuit 120 is applied to
the drive circuit 121 for the liquid crystal shutter 80.
The addition circuit 120 outputs an analog voltage at one of three
different levels in accordance with the output of the
photoelectronic device 89a. The drive circuit 121 amplifies the
analog voltage and sends it to the liquid crystal panel 80a.
Alternatively, the addition circuit 120 may be eliminated.
This modification to the transmitted light intensity control
circuit allows adjustment of the instantaneous phototransmissivity
of each liquid crystal panel 80a, 80b or 80c among three
levels.
In the third embodiment of this invention, when the strobed visible
light from the light caster 6 is off, all of the liquid crystal
panel 80a, 80b and 80c are opaque and on the other hand, when the
strobed visible light from the light caster 6 is on, each of the
liquid crystal panels 80a, 80b and 80c adjusts its duty cycle or
proper transmissivity in response to the intensity of received
light. However, a liquid crystal shutter which always is open when
the strobed visible light from the light caster 6 is on, but not
when this light is off can shield the solid state image pickup
sensor from optical noise including the high-beam headlights of a
vehicle in the opposite lane, so that adverse loss of contrast in
the picture on the display 5 can be sufficiently prevented.
According to another embodiment of this invention, the output of
each photoelectronic device of the light intensity sensor is
amplified and applied to each liquid crystal panel with a suitable
synchronous signal so that the liquid crystal panel can
proportionally adjust its transmissivity in accordance with the
intensity of received light.
According to further embodiment of this invention, the light caster
is used as an auxiliary front light rather than as a headlight.
According to yet another embodiment of this invention, the
headlight intensity can be controlled stepwise from 10 to 100%.
* * * * *